BFC 21103 Hydrology

Chapter 1. Basic Concept of Hydrology

Zarina Md AliBased on BFC 32002 Hydrology Module

Email: zarinaa@guthm.edu.my: 074564359 / 0197722315

Room: Level 6, South East Tower, FKAAS

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Topics

• Introduction to hydrology

• Hydrology cycle

• Water balance

Hydrology• Hydrology is a science that studies the availability (sources of

water) and movement of water in the earth.

• Hydrology is also defined as a science related to the occurrenceand distribution of natural water on the earth.

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Tahan River, Pahang Hot spring, Sungai Klah, Sungkai,

Perak

Importance in managing:

1) Water resources

2) Water supply management

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3) Managing floods/droughts, drainage & urban stormwater problems

Stormwater Management and Road

Tunnel (SMART), Kuala Lumpur,

Malaysia

Global Water StatisticsTotal water = 1.36 x 1018 m3

• Oceans and lakes (saltwater) 97.2%

• Ice and glaciers (fresh water) 2.15%

• Groundwater (fresh water) 0.64%

• Lakes and rivers (fresh water) 0.0085%

• Atm and biosphere (moisture) 0.00015%

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Malaysia Water Statistics Total water = 990 x 109 m3

• Lakes and rivers 566 x 109 m3

• Atm and biosphere(moisture) 360 x 109 m3

• Groundwater 64 x 109 m3

Hydrologic Cycle

Hydrologic cycle is a continues process in whichwater is evaporated from water surfaces andoceans, moves inland as moist air masses, andproduce precipitation if the correct vertical liftingconditions exist. The precipitation that falls fromclouds onto the land surface of the earth isdispersed to the hydrologic cycle via severalpathways. B

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Hydrologic cycle process

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P = PrecipitationT = TranspirationF = InfiltrationR = Run-offG = Groundwater flowLS = Land surfaceWT = Water tableE = Evaporation from lake,

land surface and ocean

Catchment/Watershed areasA watershed is a contiguous area that interceptsthe rainfall and drains to an outlet (stream orocean). It is also called as catchment or drainagearea; or drainage basin

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Water balance

• In quantitative terms, hydrology cycle can berepresented by a closed equation whichrepresents the principle of conservation of mass,often referred to in hydraulics as the continuityequation. And many forms of this expression,called the water balance.

• Water balance equation is the base of amodeling of hydrology. B

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Water budget

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Conceptual• The same concept can be applied to small basins or large

watersheds

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P – R – G – E – T = ΔS

where:

P = precipitation,

R = surface runoff,

G = groundwater flow,

E = evaporation,

T = transpiration,

ΔS = change in storage in a specified time period.

Example 1.1In April 2017, a 121 ha lake has recorded 0.43 m3/s ofinflow, 0.37 m3/s of outflow, and total storage of 1.97 ha-m.While, a USGS gage recorded a total of precipitation is 3.3cm for the lake. Assuming that infiltration loss isinsignificant for the lake, determine the evaporation lossover the lake for the month, in unit cm.

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• Solving the water balance for inflow I and outflow Q in a lake gives, for evaporation,

E = I – O + P – ΔS

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cmm 9292.0

1ha

10,000m121ha

1hour

3,600sec

1day

24hr

1month

30day1month

sec

m0.43

2

3

I

0.79 79m cm

Q

3

2

m 30day 24hr 3,600sec0.37 1month

sec 1month 1day 1hour

10,000m121ha

1ha

P = 3.3 cm

E = 92 – 79 + 3.3 – 1.63 = 14.67 cm

cm63.10163.0

121ha

m1.97haΔS

1 ha = 10000 square-m

Example 1.2

Month January February March

Inflow (m3) 4 6 9

Outflow (m3) 8 11 5

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Inflow and outflows of reservoir for the first 3 months of theyear. If the storage capacity at the early of January is 60 m3 ,calculate the storage volume at the end of March.

( I1 + I2 + I3 )/3 - (O1 + O2 + O3)/3 = S2 – S1 /3 months(4 + 6 + 9)/3 – (8 + 11 + 5 )/3 = (S2-60)/3 months

(6.33 – 8) ( 3 months) = S2 – 60 m3

-1.67 ( 3 months ) + 60 = S2 – 60 m3

S2 = 54.99 m3

Example 1.3

Day Evaporation(mm)

Rainfall(mm)

Measured Level(mm)

123456789

10

12.70

12.70

12.712.7

012.712.712.7

-25.4

-50.8

--

101.6---

1,524

1,321

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A swimming pool (6m 6m 1.5m) has a small leak at thebottom side. Data measurement of rainfall, evaporation, andwater level for 10 days which is prepared for repairingprocess. Estimate the average daily leakage out of theswimming pool in cm3/day.

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Example 1.4

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Example 1.4

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Hydrological Data Data of hydrologic variables are fundamental to analyses,forecasting, and modeling. Such data may be found innumerous publications of agencies, research institutes,universities, and other organizations. The data normallyrequired in the studies are:

• Rainfall depth - Department of Irrigation and DrainageMalaysia (DID) and Malaysian Meteorological Department

• Meteorological data (evaporation, temperature, windspeed and direction, solar radiation, and moisturecontent) - Malaysia Meteorological Department (MMD)and DID

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Hydrological Data • Stream-flow and water level - Department of Irrigation

and Drainage Malaysia (DID) and Department ofEnvironment (DOE) Malaysia

• Groundwater level - Minerals and GeoscienceDepartment Malaysia of Ministry of Natural Resourcesand Environment

• Landuse - Forestry Departments or Department ofSurvey and Mapping Malaysia

• Physical characteristics of development area -Department of Survey and Mapping Malaysia orMalaysian Remote Sensing Agency

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Conclusion

• Hydrology is the science of water.

• It embraces the occurrence, distribution,movement and properties of the waters of theearth.

• A mathematical accounting system may beconstructed for the inputs, outputs and waterstorages of a region so that a history of watermovement over time can be estimated. B

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25THANK YOU